In recent years, an imaging apparatus such as still video camera or video camera is becoming rapidly popular for electronically storing images. With such an imaging apparatus, the image of an object formed by a camera lens is converted into an electric signal for every pixel by an imaging device such as CCD and CMOS, and the result is stored in a recoding medium as image data.
With such an imaging apparatus, because the imaging device includes regularly-aligned pixels on a light reception surface, when an object for imaging has any spatial frequency component approximated to a sampling spatial frequency that is determined by pixel spacing, moiré appears in the image data of the object. Moreover, because the imaging device has the spectral sensibility different from that of human eyes and high sensibility not only for visible radiation but also for infrared radiation, there needs to remove any infrared radiation from radiation to the object. Therefore, a low-pass filter and an infrared blocking filter are generally disposed between a camera lens and an imaging device.
The issue here is that optical devices such as low-pass filter and infrared blocking filter are each made of an insulation material, and thus are easily attached with dirt and dust due to static buildup easily caused by piezoelectric effects and pyroelectric effects. There is a problem that, when these optical devices are attached with dirt and dust, the shadows of the dirt and dust are possibly captured by the imaging device. With this being the case, the closer the dirt and dust to the imaging device, the more focused the dirt and dust will be. Therefore, the dirt and dust are to be clearly perceived in the captured image. Especially with a camera such as single-lens reflex camera in which the camera lens is exchangeable, it is highly possible that the dirt and dust get into the camera at the time of lens exchange, thereby easily causing the problem as above.
In order to prevent the attachment of dirt and dust due to static buildup, a proposal has been made to form a transparent conductive film on the surface of the optical device such as low-pass filter for the aim of removing the static electricity, for example. However, if the transparent conductive film is a coating film of metal or others, the light will be reflected on the coating film of metal because the coating film of metal is high in refraction index, thereby causing a new problem of reducing the light amount of the radiation to the object entering the imaging device.
In consideration thereof, in Patent Document 1, for example, proposed is to suppress the reflection on the surface of a low-pass filter by forming a transparent conductive film on the base surface of the low-pass filter, and an antireflective film over the conductive film.    [Patent Document 1] JP-A-2002-33468